Flexible picture partitioning

ABSTRACT

Systems and methods may provide flexible picture partitioning, a method includes receiving a coded picture that is partitioned into a plurality of coding tree units (CTUs), wherein at least one row or column of CTUs, among the plurality of CTUs of the coded picture, that is adjacent to a boundary of the coded picture has a size dimension that is smaller than a corresponding size dimension of each CTU among the plurality of CTUs that is not adjacent to any boundary of the coded picture; and decoding the coded picture based on the plurality of CTUs, wherein the at least one row or column of CTUs includes a first CTU row or a first CTU column of the coded picture that is adjacent to a top boundary or left boundary of the coded picture, respectively.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.62/975,505, filed on Feb. 12, 2020, the disclosure of which isincorporated herein by reference in its entirety.

FIELD

Embodiments of the present disclosure are directed to a set of advancedvideo coding technologies. More specifically, embodiments of the presentdisclosure may provide flexible picture partitioning.

BACKGROUND

AOMedia Video 1 (AV1) is an open video coding format designed for videotransmissions over the Internet. It was developed as a successor to VP9by the Alliance for Open Media (AOMedia), a consortium founded in 2015that includes semiconductor firms, video on demand providers, videocontent producers, software development companies, and web browservendors. Many of the components of the AV1 project were sourced fromprevious research efforts by Alliance members. Individual contributorsstarted experimental technology platforms years before: Xiph's/Mozilla'sDaala published code in 2010, Google's experimental VP9 evolutionproject VP10 was announced on Sep. 12, 2014, and Cisco's Thor waspublished on Aug. 11, 2015. Building on the codebase of VP9, AV1incorporates additional techniques, several of which were developed inthese experimental formats. The first version, version 0.1.0, of the AV1reference codec was published on Apr. 7, 2016. The Alliance announcedthe release of the AV1 bitstream specification on Mar. 28, 2018, alongwith a reference, software-based encoder and decoder. On Jun. 25, 2018,a validated version 1.0.0 of the specification was released. On Jan. 8,2019, “AV1 Bitstream & Decoding Process Specification” was released,which is a validated version 1.0.0 with Errata 1 of the specification.The AV1 bitstream specification includes a reference video codec. The“AV1 Bitstream & Decoding Process Specification” (Version 1.0.0 withErrata 1), The Alliance for Open Media (Jan. 8, 2019), is incorporatedherein in its entirety by reference.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) publishedversion 1 of the H.265/HEVC (High Efficiency Video Coding) standard in2013, version 2 in 2014, version 3 in 2015, and version 4 in 2016. In2015, these two standard organizations jointly formed the Joint VideoExploration Team (JVET) to explore the potential of developing the nextvideo coding standard beyond HEVC. In October 2017, JVET issued theJoint Call for Proposals on Video Compression with Capability beyondHEVC (CfP). By Feb. 15, 2018, total 22 CfP responses on standard dynamicrange (SDR), 12 CfP responses on high dynamic range (HDR), and 12 CfPresponses on 360 video categories were submitted, respectively. In April2018, all received CfP responses were evaluated in the 122 MPEG/10thJVET meeting. As a result of this meeting, JVET formally launched thestandardization process of next-generation video coding beyond HEVC. Thenew standard was named Versatile Video Coding (VVC), and JVET wasrenamed as Joint Video Expert Team. The specification for the VVCstandard, “Versatile Video Coding (Draft 7)”, JVET-P2001-vE, Joint VideoExperts Team (October 2019), is incorporated herein in its entirety byreference.

SUMMARY

In modern video coding standards, such as H.264/AVC, HEVC, VVC, and AV1,a picture is divided into a sequence of CTUs with raster scan order,wherein the size of the CTUs are the same with each other except thoselocated at the right or bottom boundary of the picture. However, if theobject boundary is not aligned with this fixed picture partitioning, itwill need more bits to signal the boundary and motion of the object.

Some embodiments of the present disclosure address the above problemsand other problems.

According to one or more embodiments, a method performed by at least oneprocessor is provided. The method may include: receiving a coded picturethat is partitioned into a plurality of coding tree units (CTUs),wherein at least one row or column of CTUs, among the plurality of CTUsof the coded picture, that is adjacent to a boundary of the codedpicture has a size dimension that is smaller than a corresponding sizedimension of each CTU among the plurality of CTUs that is not adjacentto any boundary of the coded picture; and decoding the coded picturebased on the plurality of CTUs, wherein the at least one row or columnof CTUs includes a first CTU row or a first CTU column of the codedpicture that is adjacent to a top boundary or left boundary of the codedpicture, respectively.

According to an embodiment, each CTU among the plurality of CTUs that isnot adjacent to any boundary of the coded picture has a same size.

According to an embodiment, the at least one row or column of CTUsincludes the first CTU column that is adjacent to the left boundary ofthe coded picture and a last CTU column that is adjacent to a rightboundary of the coded picture, and the first CTU column and the last CTUcolumn each have a width that is smaller than a width of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture.

According to an embodiment, the at least one row or column of CTUsincludes or further includes the first CTU row that is adjacent to thetop boundary of the coded picture and a last CTU row that is adjacent toa bottom boundary of the coded picture, and the first CTU row and thelast CTU row each have a height that is smaller than a height of eachCTU among the plurality of CTUs that is not adjacent to any boundary ofthe coded picture.

According to an embodiment, the decoding the coded picture includessignaling the size dimension of the first CTU row or the first CTUcolumn, from among the at least one row or column of CTUs, that isadjacent to the top boundary or the left boundary of the coded picture.

According to an embodiment, the size dimension of the first CTU row orthe first CTU column is a positive integer that is a power of 2.

According to an embodiment, the decoding the coded picture includes:signaling a first flag that indicates whether the size dimension of thefirst CTU row or the first CTU column, from among the at least one rowor column of CTUs, that is adjacent to the left boundary or the topboundary of the coded picture is equal to a maximum allowed CTU size;determining, based on the first flag, that the size dimension of thefirst CTU row or the first CTU column is not equal to the maximumallowed CTU size; and signaling, based on the determining, a second flagthat indicates the size dimension of the first CTU row or the first CTUcolumn.

According to an embodiment, the decoding the coded picture includes:disallowing horizontal or vertical splitting at CTU level in the firstCTU row or the first CTU column of the coded picture, from among theleast one row or column of CTUs, based on determining that the sizedimension of the first CTU row or the first CTU column is equal to orlarger than a predetermined value and another size dimension of thefirst CTU row or the first CTU column from among the least one row orcolumn of CTUs is smaller than the predetermined value, wherein the sizedimension is one from among height and width, and the another sizedimension is the other from among the height and the width, and thepredetermined value is a power of 2 value that is greater than 64.

According to an embodiment, the decoding the coded picture includes:disallowing horizontal triple tree (TT) or vertical TT splitting at CTUlevel in the first CTU row or the first CTU column of the coded picture,from among the least one row or column of CTUs, based on determiningthat the size dimension of the first CTU row or the first CTU column isequal to or larger than a predetermined value and another size dimensionof the first CTU row or the first CTU column from among the least onerow or column of CTUs is smaller than the predetermined value, whereinthe size dimension is one from among height and width, and the anothersize dimension is the other from among the height and the width, and thepredetermined value is a power of 2 value that is greater than 64.

According to embodiments, a height of the first or last CTU row issmaller than a maximum CTU size, and each CTU among the plurality ofCTUs that is not adjacent to any boundary of the coded picture has aheight that is equal to the maximum CTU size, a decision on whether thefirst or last CTU row is smaller than other CTUs is indicated by onesyntax in a bitstream, or a width of the first or last CTU column issmaller than the maximum CTU size, and each CTU among the plurality ofCTUs that is not adjacent to any boundary of the coded picture has awidth that is equal to the maximum CTU size, a decision on whether thefirst or last CTU column is smaller than other CTUs is indicated by onesyntax in the bitstream.

According to one or more embodiments, a system is provided. The systemincludes: at least one memory configured to store computer program code;and at least one processor configured to access the computer programcode and operate as instructed by the computer program code, thecomputer program code including: decoding code configured to cause theat least one processor to decode a coded picture that is partitionedinto a plurality of coding tree units (CTUs). At least one row or columnof CTUs, among the plurality of CTUs of the coded picture, that isadjacent to a boundary of the coded picture may have a size dimensionthat is smaller than a corresponding size dimension of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture, the decoding code may be configured to cause the at least oneprocessor to decode the coded picture based on the plurality of CTUs,and the at least one row or column of CTUs may include a first CTU rowor a first CTU column of the coded picture that is adjacent to a topboundary or left boundary of the coded picture, respectively.

According to an embodiment, each CTU among the plurality of CTUs that isnot adjacent to any boundary of the coded picture has a same size.

According to an embodiment, the at least one row or column of CTUsincludes the first CTU column that is adjacent to the left boundary ofthe coded picture and a last CTU column that is adjacent to a rightboundary of the coded picture, and the first CTU column and the last CTUcolumn each have a width that is smaller than a width of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture.

According to an embodiment, the at least one row or column of CTUsincludes or further includes the first CTU row that is adjacent to thetop boundary of the coded picture and a last CTU row that is adjacent toa bottom boundary of the coded picture, and the first CTU row and thelast CTU row each have a height that is smaller than a height of eachCTU among the plurality of CTUs that is not adjacent to any boundary ofthe coded picture.

According to an embodiment, the decoding code is further configured tocause the at least one processor to signal the size dimension of thefirst CTU row or the first CTU column, from among the at least one rowor column of CTUs, that is adjacent to the top boundary or the leftboundary of the coded picture.

According to an embodiment, the decoding code is further configured tocause the at least one processor to: signal a first flag that indicateswhether the size dimension of the first CTU row or the first CTU column,from among the at least one row or column of CTUs, that is adjacent tothe left boundary or the top boundary of the coded picture is equal to amaximum allowed CTU size; based on the first flag, that the sizedimension of the first CTU row or the first CTU column is not equal tothe maximum allowed CTU size; and signal, based on the determining, asecond flag that indicates the size dimension of the first CTU row orthe first CTU column.

According to an embodiment, the decoding code is further configured tocause the at least one processor to: disallow horizontal or verticalsplitting at CTU level in the first CTU row or the first CTU column ofthe coded picture, from among the least one row or column of CTUs, basedon determining that the size dimension of the first CTU row or the firstCTU column is equal to or larger than a predetermined value and anothersize dimension of the first CTU row or the first CTU column from amongthe least one row or column of CTUs is smaller than the predeterminedvalue, wherein the size dimension is one from among height and width,and the another size dimension is the other from among the height andthe width, and the predetermined value is a power of 2 value that isgreater than 64.

According to an embodiment, the decoding code is further configured tocause the at least one processor to: disallow horizontal triple tree(TT) or vertical TT splitting at CTU level in the first CTU row or thefirst CTU column of the coded picture, from among the least one row orcolumn of CTUs, based on determining that the size dimension of thefirst CTU row or the first CTU column is equal to or larger than apredetermined value and another size dimension of the first CTU row orthe first CTU column from among the least one row or column of CTUs issmaller than the predetermined value, wherein the size dimension is onefrom among height and width, and the another size dimension is the otherfrom among the height and the width, and the predetermined value is apower of 2 value that is greater than 64.

According to one or more embodiments, a non-transitory computer-readablemedium storing computer instructions is provided. The computerinstructions may be configured to, when executed by at least oneprocessor, cause the at least one processor to: decode a coded picturethat is partitioned into a plurality of coding tree units (CTUs),wherein at least one row or column of CTUs, among the plurality of CTUsof the coded picture, that is adjacent to a boundary of the codedpicture has a size dimension that is smaller than a corresponding sizedimension of each CTU among the plurality of CTUs that is not adjacentto any boundary of the coded picture, the computer instructions areconfigured to cause the at least one processor to decode the codedpicture based on the plurality of CTUs, and the at least one row orcolumn of CTUs includes a first CTU row or a first CTU column of thecoded picture that is adjacent to a top boundary or left boundary of thecoded picture, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 is an example illustration of a picture divided into CTUs.

FIG. 6A is an example illustration of a block for describing a firstexample of partition restrictions in VTM.

FIG. 6B is an example illustration of a block for describing a secondexample of partition restrictions in VTM.

FIG. 6C is an example illustration of a block for describing a thirdexample of partition restrictions in VTM.

FIG. 6D is an example illustration of a block for describing a fourthexample of partition restrictions in VTM.

FIG. 6E is an example illustration of a block for describing a fifthexample of partition restrictions in VTM.

FIG. 6F is an example illustration of a block for describing a sixthexample of partition restrictions in VTM.

FIG. 6G is an example illustration of a block for describing a seventhexample of partition restrictions in VTM.

FIG. 6H is an example illustration of a block for describing an eighthexample of partition restrictions in VTM.

FIG. 7A is a diagram for demonstrating vertical binary splitting type ina multi-type tree structure.

FIG. 7B is a diagram for demonstrating horizontal binary splitting typein a multi-type tree structure.

FIG. 7C is a diagram for demonstrating vertical ternary splitting typein a multi-type tree structure.

FIG. 7D is a diagram for demonstrating horizontal ternary splitting typein a multi-type tree structure.

FIG. 8 is a diagram illustrating a signalling mechanism of partitionsplitting information in quadtree with nested multi-type tree codingtree structure.

FIG. 9 is an example diagram illustrating a CTU divided into multipleCUs with a quadtree and nested multi-type tree coding block structure.

FIG. 10A a diagram illustrating a first example partition structure ofVP9.

FIG. 10B a diagram illustrating a second example partition structure ofVP9.

FIG. 10C a diagram illustrating a third example partition structure ofVP9.

FIG. 10D a diagram illustrating a fourth example partition structure ofVP9.

FIG. 11A a diagram illustrating a first example partition structure ofAV1.

FIG. 11B a diagram illustrating a second example partition structure ofAV1.

FIG. 11C a diagram illustrating a third example partition structure ofAV1.

FIG. 11D a diagram illustrating a fourth example partition structure ofAV1.

FIG. 11E a diagram illustrating a fifth example partition structure ofAV1.

FIG. 11F a diagram illustrating a sixth example partition structure ofAV1.

FIG. 11G a diagram illustrating a seventh example partition structure ofAV1.

FIG. 11H a diagram illustrating an eighth example partition structure ofAV1.

FIG. 11I a diagram illustrating a ninth example partition structure ofAV1.

FIG. 11J a diagram illustrating a tenth example partition structure ofAV1.

FIG. 12 is a diagram illustrating a picture divided into a plurality ofCTUs according to an embodiment of the present disclosure.

FIG. 13 is a diagram illustrating a picture divided into a plurality ofCTUs according to an embodiment of the present disclosure.

FIG. 14 is a diagram illustrating a picture divided into a plurality ofCTUs according to an embodiment of the present disclosure.

FIG. 15 is a diagram illustrating a picture divided into a plurality ofCTUs according to an embodiment of the present disclosure.

FIG. 16 is a schematic diagram of a decoder according to an embodimentof the present disclosure.

FIG. 17 is a diagram of a computer system suitable for implementingembodiments of the present disclosure.

DETAILED DESCRIPTION

[Partitioning of the Picture into CTUs]

Pictures may be divided into a sequence of coding tree units (CTUs),which may also be called super blocks (SBs). The CTU concept in HEVC andVVC is similar to the SB concept in AV1. For a picture that has threesample arrays, a CTU may comprise or consist of an N×N block of lumasamples together with two corresponding blocks of chroma samples. FIG. 5shows an example of a picture (500) divided into CTUs (510).

The maximum allowed size of the luma block in a CTU is specified to be128×128 (although the maximum size of luma transform blocks is 64×64).

Virtual pipeline data units (VPDUs) may be defined as non-overlappingunits in a picture. In hardware decoders, successive VPDUs may beprocessed by multiple pipeline stages at the same time. The VPDU size isroughly proportional to the buffer size in most pipeline stages, so itmay be important to keep the VPDU size small. In most hardware decoders,the VPDU size can be set to maximum transform block (TB) size.

In order to keep the VPDU size as 64×64 luma samples, the followingnormative partition restrictions (with syntax signaling modification)may be applied in VVC Test Model (VTM), as shown in FIGS. 6A-H, whichillustrate a block (520) of a CTU having a size of 128×128, wherein theblock (520) is partitioned into four VPDUs indicated with thin lines,and disallowed partitioning for CUs is indicated with partition lines(527):

-   -   Triple tree (TT) split is not allowed for a CU when one or both        of the width or height of the CU is equal to 128. For example,        TT split may not be allowed for the CUs as indicated in FIGS.        6A-B and 6E-H.    -   For a 128×N CU with N≤64 (i.e. width equal to 128 and height        smaller than or equal to 128), horizontal binary tree (BT) is        not allowed. For example, horizontal BT split may not be allowed        for the CUs as indicated in FIG. 6D.    -   For an N×128 CU with N≤64 (i.e. height equal to 128 and width        smaller than or equal to 64), vertical BT is not allowed. For        example, vertical BT split may not be allowed for the CUs as        indicated in FIG. 6C.

In HEVC and VVC, when a portion of a tree node block exceeds the bottomor right picture boundary, the tree node block may be forced to be splituntil all samples of every coded CU are located inside the pictureboundaries.

[Quadtree with Nested Multi-Type Tree Coding Block Structure in VVC]

In HEVC, a CTU may be split into CUs by using a quad tree (QT) structuredenoted as coding tree to adapt to various local characteristics. Thedecision on whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction may be made at the CUlevel. Each CU can be further split into one, two, or four predictionunits (PUs) according to the PU splitting type. Inside one PU, the sameprediction process may be applied, and the relevant information istransmitted to the decoder on a PU basis. After obtaining the residualblock by applying the prediction process based on the PU splitting type,a CU can be partitioned into transform units (TUs) according to anotherquadtree structure like the coding tree for the CU. One of key featuresof the HEVC structure is that it has the multiple partition conceptsincluding CU, PU, and TU.

In VVC, a quadtree with nested multi-type tree using binary and ternarysplits segmentation structure replaces the concepts of multiplepartition unit types. That is, VVS does not include the separation ofthe CU, PU, and TU concepts except as needed for CUs that have a sizetoo large for the maximum transform length, and supports moreflexibility for CU partition shapes. In the coding tree structure, a CUcan have either a square or rectangular shape. A coding tree unit (CTU)is first partitioned by a quaternary tree (a.k.a. quadtree) structure.Then, the quaternary tree leaf nodes can be further partitioned by amulti-type tree structure. As shown in diagrams (550)-(580) of FIGS.7A-D, there are four splitting types in multi-type tree structure:vertical binary splitting (SPLIT_BT_VER) as illustrated in FIG. 7A,horizontal binary splitting (SPLIT_BT_HOR) as illustrated in FIG. 7B,vertical ternary splitting (SPLIT_TT_VER) as illustrated in FIG. 7C, andhorizontal ternary splitting (SPLIT_TT_HOR) as illustrated in FIG. 7D.The multi-type tree leaf nodes may be called coding units (CUs), andunless the CU is too large for the maximum transform length, thissegmentation may be used for prediction and transform processing withoutany further partitioning. This means that, in most cases, the CU, PU,and TU have the same block size in the quadtree with nested multi-typetree coding block structure. The exception occurs when maximum supportedtransform length is smaller than the width or height of the colorcomponent of the CU.

FIG. 8 illustrates a signalling mechanism of the partition splittinginformation in quadtree with nested multi-type tree coding treestructure. A coding tree unit (CTU) (605) may be treated as the root ofa quaternary tree and may be first partitioned by a quaternary treestructure based on a flag (612) (qt_split_flag) that is signalled. Forexample, when the value of the first flag (612) is “1”, a quadtreepartitioning may not be performed such that there are QT_nodes (610).When the value of the first flag (612) is “0”, the quadtree partitioningmay be performed such that there is one or more of a quaternary treeleaf node (615) (QT-leaf_node/MTT_node). Each quaternary tree leaf node(615) (when sufficiently large to allow it) is then further partitionedby a multi-type tree structure. In the multi-type tree structure, a flag(617) (mtt_split_cu_flag or mtt_split_flag) is signalled to indicatewhether the quaternary tree leaf node (615) is further partitioned. Forexample, when a value of the flag 617 is “1”, a quaternary tree leafnode (615) is further partitioned (indicated by reference character620). And when the value of the flag (617) is “0”, the quaternary treeleaf node (615) is not further partitioned (indicate by referencecharacter 625). If the quaternary tree leaf node (615) is furtherpartitioned, a flag (622) (mtt_split_cu_vertical_flag ormtt_split_vertical_flag) may be signalled to indicate the splittingdirection. For example, if the value of the flag (622) is “1”, thequaternary tree leaf node (615) may be vertically split (indicated byreference character 630), and if the value of the flag (622) is “0”, thequaternary tree leaf node (615) may be horizontally split (indicated byreference character 635). A flag (632) (mtt_split_cu_binary_flag ormtt_split_binary_flag) may be signalled to indicate whether the split isa binary split or a ternary split. For example, if the value of the flag(632) is “1”, the quaternary tree leaf node (615) may be binary split(indicated by reference characters 640 and 650), and if the value of theflag (632) is “0”, the quaternary tree leaf node (615) may be ternarysplit (indicated by reference characters 645 and 655). Based on thevalues of the flag (622) and the flag (632), the multi-type treesplitting mode (MttSplitMode) of a CU may be derived as shown below inTABLE 1.

TABLE 1 MttSplitMode derviation based on multi-type tree syntax elementsMttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flagSPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

FIG. 9 shows a CTU (660) divided into multiple CUs with a quadtree andnested multi-type tree coding block structure, where the bold line edgesrepresent quadtree partitioning and the broken line edges representmulti-type tree partitioning. The quadtree with nested multi-type treepartition provides a content-adaptive coding tree structure comprised ofCUs. The size of the CU(s) may be as large as the CTU or as small as 4×4in units of luma samples. For the case of the 4:2:0 chroma format, themaximum chroma CB size is 64×64 and the minimum chroma CB size is 2×2.

In VVC, the maximum supported luma transform size is 64×64 and themaximum supported chroma transform size is 32×32. When the width orheight of the CB is larger than the maximum transform width or height,the CB is automatically split in the horizontal and/or verticaldirection to meet the transform size restriction in that direction.

In VTM7, the coding tree scheme supports the ability for the luma andchroma to have a separate block tree structure. For P and B slices, theluma and chroma CTBs in one CTU have to share the same coding treestructure. However, for I slices, the luma and chroma can have separateblock tree structures. When separate block tree mode is applied, lumaCTB is partitioned into CUs by one coding tree structure, and the chromaCTBs are partitioned into chroma CUs by another coding tree structure.This means that a CU in an I slice may consist of a coding block of theluma component or coding blocks of two chroma components, and a CU in aP or B slice may consist of coding blocks of all three colour componentsunless the video is monochrome.

[Coding Block Partition in VP9 and AV1]

With reference to partition structures (670)-(673) of FIGS. 10A-D, VP9uses a 4-way partition tree starting from the 64×64 level down to 4×4level, with some additional restrictions for blocks 8×8. Note thatpartitions designated as R in FIG. 10D refer to recursion in that thesame partition tree is repeated at a lower scale until the lowest 4×4level is reached.

With reference to partition structures (680)-(689) of FIGS. 11A-J, AV1not only expands the partition-tree to a 10-way structure, but alsoincreases the largest size (referred to as superblock in VP9/AV1parlance) to start from 128×128. Note that this includes 4:1/1:4rectangular partitions that did not exist in VP9. None of therectangular partitions can be further subdivided. In addition to codingblock size, coding tree depth is defined to indicate the splitting depthfrom the root note. To be specific, the coding tree depth for the rootnode, e.g. 128×128, is set to 0, and after tree block is further splitonce, the coding tree depth is increased by 1.

Instead of enforcing fixed transform unit sizes as in VP9, AV1 allowsluma coding blocks to be partitioned into transform units of multiplesizes that can be represented by a recursive partition going down by upto 2 levels. To incorporate AV1's extended coding block partitions,square, 2:1/1:2, and 4:1/1:4 transform sizes from 4×4 to 64×64 may besupported. For chroma blocks, only the largest possible transform unitsmay be allowed.

Embodiments of the present disclosure are discussed in detail below. Theterm “CTU” as used below in this disclosure may refer to a largestcoding unit (LCU) of a coding standard. For example, the term “CTU” mayrefer to a CTU as defined in HEVC and VVC and/or an SB as defined inAV1.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110, 120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data, and maydisplay the recovered video data at a local display device.

In FIG. 1, the terminals (110-140) may be illustrated as servers,personal computers, and smart phones, and/or any other type of terminal.For example, the terminals (110-140) may be laptop computers, tabletcomputers, media players and/or dedicated video conferencing equipment.The network (150) represents any number of networks that convey codedvideo data among the terminals (110-140), including for example wirelineand/or wireless communication networks. The communication network (150)may exchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks, and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(150) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

As illustrated in FIG. 2, a streaming system (200) may include a capturesubsystem (213) that can include a video source (201) and an encoder(203). The video source (201) may be, for example, a digital camera, andmay be configured to create an uncompressed video sample stream (202).The uncompressed video sample stream (202) may provide a high datavolume when compared to encoded video bitstreams, and can be processedby the encoder (203) coupled to the camera (201). The encoder (203) caninclude hardware, software, or a combination thereof to enable orimplement aspects of the disclosed subject matter as described in moredetail below. The encoded video bitstream (204) may include a lower datavolume when compared to the sample stream, and can be stored on astreaming server (205) for future use. One or more streaming clients(206) can access the streaming server (205) to retrieve video bitstreams (209) that may be copies of the encoded video bitstream (204).

In embodiments, the streaming server (205) may also function as aMedia-Aware Network Element (MANE). For example, the streaming server(205) may be configured to prune the encoded video bitstream (204) fortailoring potentially different bitstreams to one or more of thestreaming clients (206). In embodiments, a MANE may be separatelyprovided from the streaming server (205) in the streaming system (200).

The streaming clients (206) can include a video decoder (210) and adisplay (212). The video decoder (210) can, for example, decode videobitstream (209), which is an incoming copy of the encoded videobitstream (204), and create an outgoing video sample stream (211) thatcan be rendered on the display (212) or another rendering device (notdepicted). In some streaming systems, the video bitstreams (204, 209)can be encoded according to certain video coding/compression standards.Examples of such standards include, but are not limited to, ITU-TRecommendation H.265. Under development is a video coding standardinformally known as Versatile Video Coding (VVC). Embodiments of thedisclosure may be used in the context of VVC.

FIG. 3 illustrates an example functional block diagram of a videodecoder (210) that is attached to a display (212) according to anembodiment of the present disclosure.

The video decoder (210) may include a channel (312), receiver (310), abuffer memory (315), an entropy decoder/parser (320), a scaler/inversetransform unit (351), an intra prediction unit (352), a MotionCompensation Prediction unit (353), an aggregator (355), a loop filterunit (356), reference picture memory (357), and current picture memory(). In at least one embodiment, the video decoder (210) may include anintegrated circuit, a series of integrated circuits, and/or otherelectronic circuitry. The video decoder (210) may also be partially orentirely embodied in software running on one or more CPUs withassociated memories.

In this embodiment, and other embodiments, the receiver (310) mayreceive one or more coded video sequences to be decoded by the decoder(210) one coded video sequence at a time, where the decoding of eachcoded video sequence is independent from other coded video sequences.The coded video sequence may be received from the channel (312), whichmay be a hardware/software link to a storage device which stores theencoded video data. The receiver (310) may receive the encoded videodata with other data, for example, coded audio data and/or ancillarydata streams, that may be forwarded to their respective using entities(not depicted). The receiver (310) may separate the coded video sequencefrom the other data. To combat network jitter, the buffer memory (315)may be coupled in between the receiver (310) and the entropydecoder/parser (320) (“parser” henceforth). When the receiver (310) isreceiving data from a store/forward device of sufficient bandwidth andcontrollability, or from an isosynchronous network, the buffer (315) maynot be used, or can be small. For use on best effort packet networkssuch as the Internet, the buffer (315) may be required, can becomparatively large, and can be of adaptive size.

The video decoder (210) may include a parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include, for example, information used to manage operation ofthe decoder (210), and potentially information to control a renderingdevice such as a display (212) that may be coupled to a decoder asillustrated in FIG. 2. The control information for the renderingdevice(s) may be in the form of, for example, Supplementary EnhancementInformation (SEI) messages or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The parser (320) may also extractfrom the coded video sequence information such as transformcoefficients, quantizer parameter values, motion vectors, and so forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how they are involved, can be controlledby the subgroup control information that was parsed from the coded videosequence by the parser (320). The flow of such subgroup controlinformation between the parser (320) and the multiple units below is notdepicted for clarity.

Beyond the functional blocks already mentioned, decoder (210) can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

One unit may be the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) may receive quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). The scaler/inversetransform unit (351) can output blocks including sample values that canbe input into the aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture fromthe current picture memory (358). The aggregator (355), in some cases,adds, on a per sample basis, the prediction information the intraprediction unit (352) has generated to the output sample information asprovided by the scaler/inverse transform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (351) (in this case called the residual samples orresidual signal) so to generate output sample information. The addresseswithin the reference picture memory (357), from which the MotionCompensation Prediction unit (353) fetches prediction samples, can becontrolled by motion vectors. The motion vectors may be available to theMotion Compensation Prediction unit (353) in the form of symbols (321)that can have, for example, X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory (357) when sub-sample exactmotion vectors are in use, motion vector prediction mechanisms, and soforth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to a render device such as a display (212), as well as storedin the reference picture memory (357) for use in future inter-pictureprediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picturecan become part of the reference picture memory (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (210) may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also, for compliance with some videocompression technologies or standards, the complexity of the coded videosequence may be within bounds as defined by the level of the videocompression technology or standard. In some cases, levels restrict themaximum picture size, maximum frame rate, maximum reconstruction samplerate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (210) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 illustrates an example functional block diagram of a videoencoder (203) associated with a video source (201) according to anembodiment of the present disclosure.

The video encoder (203) may include, for example, an encoder that is asource coder (430), a coding engine (432), a (local) decoder (433), areference picture memory (434), a predictor (435), a transmitter (440),an entropy coder (445), a controller (450), and a channel (460).

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can include one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofcontroller (450). The controller (450) may also control other functionalunits as described below and may be functionally coupled to these units.The coupling is not depicted for clarity. Parameters set by thecontroller (450) can include rate control related parameters (pictureskip, quantizer, lambda value of rate-distortion optimizationtechniques, . . . ), picture size, group of pictures (GOP) layout,maximum motion vector search range, and so forth. A person skilled inthe art can readily identify other functions of controller (450) as theymay pertain to video encoder (203) optimized for a certain systemdesign.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of the source coder (430)(responsible for creating symbols based on an input picture to be coded,and a reference picture(s)), and the (local) decoder (433) embedded inthe encoder (203) that reconstructs the symbols to create the sampledata that a (remote) decoder also would create when a compressionbetween symbols and coded video bitstream is lossless in certain videocompression technologies. That reconstructed sample stream may be inputto the reference picture memory (434). As the decoding of a symbolstream leads to bit-exact results independent of decoder location (localor remote), the reference picture memory content is also bit exactbetween a local encoder and a remote encoder. In other words, theprediction part of an encoder “sees” as reference picture samplesexactly the same sample values as a decoder would “see” when usingprediction during decoding. This fundamental principle of referencepicture synchronicity (and resulting drift, if synchronicity cannot bemaintained, for example because of channel errors) is known to a personskilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3. However, as symbols are available anden/decoding of symbols to a coded video sequence by the entropy coder(445) and the parser (320) can be lossless, the entropy decoding partsof decoder (210), including channel (312), receiver (310), buffer (315),and parser (320) may not be fully implemented in the local decoder(433).

An observation that can be made at this point is that any decodertechnology, except the parsing/entropy decoding that is present in adecoder, may need to be present, in substantially identical functionalform in a corresponding encoder. For this reason, the disclosed subjectmatter focuses on decoder operation. The description of encodertechnologies can be abbreviated as they may be the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture memory (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as an Intra Picture (I picture), a Predictive Picture (Ppicture), or a Bi-directionally Predictive Picture (B Picture).

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh (IDR) Pictures. Aperson skilled in the art is aware of those variants of I pictures andtheir respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Before describing certain aspects of embodiments of the disclosure inmore detail, a few terms are introduced below that are referred to inthe remainder of this description.

“Sub-Picture” henceforth refers to, in some cases, a rectangulararrangement of samples, blocks, macroblocks, coding units, or similarentities that are semantically grouped, and that may be independentlycoded in changed resolution. One or more sub-pictures may form apicture. One or more coded sub-pictures may form a coded picture. One ormore sub-pictures may be assembled into a picture, and one or more subpictures may be extracted from a picture. In certain environments, oneor more coded sub-pictures may be assembled in the compressed domainwithout transcoding to the sample level into a coded picture, and in thesame or certain other cases, one or more coded sub-pictures may beextracted from a coded picture in the compressed domain.

“Adaptive Resolution Change” (ARC) henceforth refers to mechanisms thatallow the change of resolution of a picture or sub-picture within acoded video sequence, by the means of, for example, reference pictureresampling. “ARC parameters” henceforth refer to the control informationrequired to perform adaptive resolution change, that may include, forexample, filter parameters, scaling factors, resolutions of outputand/or reference pictures, various control flags, and so forth.

According to embodiments of the present disclosure, the size of CTUslocated in the first row (and/or column) of a picture can be smallerthan the size of the CTUs located in the second row (and/or column) ofthe picture, and the size of the CTUs may be the same except thoselocated at the top, bottom, left, and/or right picture boundaries.

For example, with reference to FIGS. 12-15, pictures (700), (710),(720), and (730) may be partitioned into a plurality of CTUs inaccordance with embodiments of the present disclosure. In FIG. 12, CTUslocated in the first CTU column (702) and last CTU column (706) of thepicture (700) may have a smaller size than the CTUs located in the othercolumns of the picture (700), and the CTUs located in the other columnsmay have a same size as each other. In FIG. 13, CTUs located in thefirst CTU row (704) and the last CTU row (708) of the picture (710) mayhave a smaller size than the CTUs located in the other rows of thepicture (710), and the CTUs located in the other rows may have a samesize as each other. In FIG. 14, CTUs located in the first CTU row (704),the first CTU column (702), the last CTU row (708), and the last CTUcolumn (706) of the picture (720) may have a smaller size than the CTUslocated in the other rows/columns of the picture (720), and the CTUslocated in the other rows/columns may have a same size as each other. InFIG. 15, CTUs located in the first CTU row (704) and the first CTUcolumn (702) may have a smaller size than the CTUs located in the otherrows/columns of the picture (730), and the CTUs located in the otherrows/columns may have a same size as each other.

In one or more embodiments, the width and/or height of the first CTU rowand/or column is signaled in High-Level Syntax (HLS) in the bitstream,such as sequence parameter set (SPS), picture parameter set (PPS), orslice header.

In one embodiment, the width and/or height of the first CTU row and/orcolumn may be signaled by using fixed length coding or truncated binaryor truncated unary coding.

In another embodiment, one flag is firstly signaled to indicate whetherthe width (and/or height) of the first CTU row (and/or column) is equalto the maximum allowed CTU size or not. If the one flag indicates thatthe width (and/or height) is not equal to the maximum allowed CTU size,a second flag may be further signaled to indicate the width (and/orheight) of the first CTU row (and/or column). In one example, fixedlength coding may be used for the signaling of second flag.

In one embodiment, the width (and/or height) of first CTU row (and/orcolumn) is restricted to power of 2, and the width (and/or height) ofthe first CTU row (and/or column) may be equal to or greater than K1,wherein K1 may be a positive integer, such as 2, 4, 6, 8, etc, or may bea power of 2. For example, the height of the first CTU row may berestricted and/or the width of the first CTU column may be restricted.

In another embodiment, the width (and/or height) of first CTU row(and/or column) may be restricted to be an integer multiple of K2,wherein K2 is an even integer, such as 2, 4, 6, 8, 10, 12, 14, 16, etc.For example, the height of the first CTU row may be restricted and/orthe width of the first CTU column may be restricted. In one embodiment,K2 may be further restricted to be a power of 2. In one embodiment, inorder to ensure the width and height of each coded block is a power of2, the same boundary handling rules for the last CTU row may be appliedto the first CTU row, and the same boundary handling rules for the lastCTU column may be applied to the first CTU column.

In one or more embodiments, when the width (and/or height) of the firstCTU row (and/or column) is equal to or larger than K3, and the height(and/or width) of the first CTU row (and/or column) is smaller than K3,then horizontal (and/or vertical) split is not allowed at CTU level inthe first CTU row (and/or column). K3 may be a power of 2 value and K3may be greater than 64, such as 128 or 256. For example, according to anembodiment, when the width of the first CTU row (704) is equal to orlarger than K3 and the height of the first CTU row (704) is smaller thanK3, then horizontal split may be prohibited at CTU level for the firstCTU row (704). Alternatively or additionally, when the height of thefirst CTU column (702) is equal to or larger than K3 and the width ofthe first CTU column (702) is smaller than K3, then vertical split maynot be prohibited at CTU level for the first CTU column (702). In a casewhere the above conditions for the first CTU row (704) and the first CTUcolumn (702) are respectively true, horizontal and vertical split of acorner CTU (709) (see FIG. 15) may be prohibited. Similarly, horizontaland vertical split of any other corner CTU may be prohibited when theCTU row and column in which the other corner CTU is provided meets theabove conditions.

In one or more embodiments, when the width (and/or height) of the firstCTU row (and/or column) is equal to or larger than K3, and the height(and/or width) of the first CTU row (and/or column) is smaller than K3,then vertical TT (and/or horizontal TT) split may not be allowed at CTUlevel in the first CTU row (and/or column). K3 may be a power of 2 valueand K3 may be greater than 64, such as 128 or 256. For example,according to an embodiment, when the width of the first CTU row (704) isequal to or larger than K3 and the height of the first CTU row (704) issmaller than K3, then horizontal TT split may be prohibited at CTU levelfor the first CTU row (704). Alternatively or additionally, when theheight of the first CTU column (702) is equal to or larger than K3 andthe width of the first CTU column (702) is smaller than K3, thenvertical TT split may be prohibited at CTU level for the first CTUcolumn (702). In a case where the above conditions for the first CTU row(704) and the first CTU column (702) are respectively true, horizontaland vertical TT split of a corner CTU (709) (see FIG. 15) may beprohibited. Similarly, horizontal and vertical TT split of any othercorner CTU may be prohibited when the CTU row and column in which theother corner CTU is provided meets the above conditions.

In one or more embodiments, only the height (and/or width) of the firstor last CTU rows (and/or columns) of a picture can be smaller than themaximum CTU size, the size of other CTU rows (and/or columns) of thepicture may be the same as the maximum CTU size. For example, as shownin FIG. 14, the height of the first CTU row (704) and the width of thefirst CTU column (702) of the picture (740) may be smaller than themaximum CTU size, and the other rows/columns of the picture (720) may beequal to the maximum CTU size.

In an embodiment, one flag is signaled in High-Level Syntax (HLS) in thebitstream, such as sequence parameter set (SPS), picture parameter set(PPS), or slice header, to indicate whether the first and/or last CTUrow (and/or column) has a smaller size than other CTU rows (and/orcolumns).

Embodiments of the present disclosure described above may apply tospecified color components only (e.g., luma only, chroma only), or applyto different color components differently (e.g., different sizes offirst CTU row or CTU column can be applied for different colorcomponents).

According to embodiments, the width of the first CTU column may bederived by the decoder from other remaining CTUs. According toembodiments, an encoder may specify the size of the first CTU column(and/or row) and/or middle column(s) (and or row(s)) to the decoder, andthe decoder may derive a size of the last CTU column (and/or row) basedon the size(s) specified.

Embodiments of the present disclosure may comprise at least oneprocessor and memory storing computer instructions. The computerinstructions, when executed by the at least one processor, may beconfigured to cause the at least one processor to perform the functionsof the embodiments of the present disclosure.

For example, with reference to FIG. 16, a decoder (800) of the presentdisclosure may comprise at least one processor and memory storingcomputer instructions. The computer instructions may comprise decodingcode (810). The decoder (800) may implement the video decoder (210)illustrated in FIGS. 2-3.

The decoding code (810) may be configured to cause the at least oneprocessor to decode a coded picture that is partitioned into a pluralityof CTUs, wherein the decoding code (810) may be configured to cause theat least one processor to decode the coded picture based on theplurality of CTUs.

The CTUs may have any of the CTU configurations of embodiments describedin the present disclosure such as, for example, with respect to FIGS.12-15. For example, at least one row or column of CTUs, among theplurality of CTUs of the coded picture, that is adjacent to a boundaryof the coded picture may have a size dimension that is smaller than acorresponding size dimension of each CTU among the plurality of CTUsthat is not adjacent to any boundary of the coded picture.

The decoding code (810) may be further configured to cause the at leastone processor to signal flags in accordance with embodiments of thepresent disclosure. For example, the decoding code (810) may beconfigured to cause the at least one processor to signal the sizedimension of a first row and/or column, from among the least one row orcolumn of CTUs, that is adjacent to the top boundary or the leftboundary of the coded picture. Alternatively, the decoding code (810)may be configured to cause the at least one processor to: signal a firstflag that indicates whether the size dimension of a first row and/orcolumn, from among the least one row or column of CTUs, that is adjacentto the left boundary or the top boundary of the coded picture is equalto a maximum allowed CTU size; determine, based on the first flag, thatthe size dimension of the first row and/or column of CTUs is not equalto the maximum allowed CTU size; and signal, based on the determining, asecond flag that indicates the size dimension of the first row and/orcolumn of CTUs.

The decoding code (810) may be further configured to cause the at leastone processor to disallow horizontal or vertical splitting at CTU leveland/or disallow horizontal triple tree (TT) or vertical TT splittingbased on the disallowance conditions of embodiments described in thepresent disclosure. For example, the decoding code (810) may beconfigured to cause the at least one processor to disallow horizontal orvertical splitting at CTU level in the first CTU row or the first CTUcolumn of the coded picture, from among the least one row or column ofCTUs, based on determining that the size dimension of the first CTU rowor the first CTU column is equal to or larger than a predetermined valueand another size dimension of the first CTU row or the first CTU columnfrom among the least one row or column of CTUs is smaller than thepredetermined value, wherein the size dimension is one from among heightand width, and the another size dimension is the other from among theheight and the width, and the predetermined value is a power of 2 valuethat is greater than 64. Alternatively or additionally, the decodingcode (810) may be configured to cause the at least one processor todisallow horizontal triple tree (TT) or vertical TT splitting at CTUlevel in the first CTU row or the first CTU column of the coded picture,from among the least one row or column of CTUs, based on determiningthat the size dimension of the first CTU row or the first CTU column isequal to or larger than a predetermined value and another size dimensionof the first CTU row or the first CTU column from among the least onerow or column of CTUs is smaller than the predetermined value, whereinthe size dimension is one from among height and width, and the anothersize dimension is the other from among the height and the width, and thepredetermined value is a power of 2 value that is greater than 64.

According to embodiments, the decoding code (810) may also be configuredto cause the at least one processor to partition the coded picture intothe plurality of CTUs.

According to embodiments, the encoder-side processes corresponding tothe above processes may be implemented by encoding code for encoding apicture as would be understood by a person of ordinary skill in the art,based on the above descriptions.

The techniques of embodiments of the present disclosure described above,can be implemented as computer software using computer-readableinstructions and physically stored in one or more computer-readablemedia. For example, FIG. 17 shows a computer system (900) suitable forimplementing embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 17 for computer system (900) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (900).

Computer system (900) may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (901), mouse (902), trackpad (903), touchscreen (910), data-glove, joystick (905), microphone (906), scanner(907), and camera (908).

Computer system (900) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (910), data-glove, or joystick (905), but there can also betactile feedback devices that do not serve as input devices). Forexample, such devices may be audio output devices (such as: speakers(909), headphones (not depicted)), visual output devices (such asscreens (910) to include CRT screens, LCD screens, plasma screens, OLEDscreens, each with or without touch-screen input capability, each withor without tactile feedback capability—some of which may be capable tooutput two dimensional visual output or more than three dimensionaloutput through means such as stereographic output; virtual-realityglasses (not depicted), holographic displays and smoke tanks (notdepicted)), and printers (not depicted).

Computer system (900) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(920) with CD/DVD or the like media (921), thumb-drive (922), removablehard drive or solid state drive (923), legacy magnetic media such astape and floppy disc (not depicted), specialized ROM/ASIC/PLD baseddevices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (900) can also include interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (949) (such as, for example USB ports of thecomputer system (900); others are commonly integrated into the core ofthe computer system 900 by attachment to a system bus as described below(for example Ethernet interface into a PC computer system or cellularnetwork interface into a smartphone computer system). Using any of thesenetworks, computer system (900) can communicate with other entities.Such communication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Such communicationcan include communication to a cloud computing environment (955).Certain protocols and protocol stacks can be used on each of thosenetworks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces (954) can be attached to a core (940) ofthe computer system (900).

The core (940) can include one or more Central Processing Units (CPU)(941), Graphics Processing Units (GPU) (942), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(943), hardware accelerators (944) for certain tasks, and so forth.These devices, along with Read-only memory (ROM) (945), Random-accessmemory (946), internal mass storage such as internal non-user accessiblehard drives, SSDs, and the like (947), may be connected through a systembus (948). In some computer systems, the system bus (948) can beaccessible in the form of one or more physical plugs to enableextensions by additional CPUs, GPU, and the like. The peripheral devicescan be attached either directly to the core's system bus (948), orthrough a peripheral bus (949). Architectures for a peripheral businclude PCI, USB, and the like. A graphics adapter (950) may be includedin the core (940).

CPUs (941), GPUs (942), FPGAs (943), and accelerators (944) can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(945) or RAM (946). Transitional data can be also be stored in RAM(946), whereas permanent data can be stored for example, in the internalmass storage (947). Fast storage and retrieve to any of the memorydevices can be enabled through the use of cache memory, that can beclosely associated with one or more CPU (941), GPU (942), mass storage(947), ROM (945), RAM (946), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (900), and specifically the core (940) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (940) that are of non-transitorynature, such as core-internal mass storage (947) or ROM (945). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (940). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(940) and specifically the processors therein (including CPU, GPU, FPGA,and the like) to execute particular processes or particular parts ofparticular processes described herein, including defining datastructures stored in RAM (946) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (944)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several non-limiting exampleembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of the disclosure. It will thusbe appreciated that those skilled in the art will be able to devisenumerous systems and methods which, although not explicitly shown ordescribed herein, embody the principles of the disclosure and are thuswithin the spirit and scope thereof.

What is claimed is:
 1. A method performed by at least one processor, themethod comprising: receiving a coded picture that is partitioned into aplurality of coding tree units (CTUs), wherein at least one row orcolumn of CTUs, among the plurality of CTUs of the coded picture, thatis adjacent to a boundary of the coded picture has a size dimension thatis smaller than a corresponding size dimension of each CTU among theplurality of CTUs that is not adjacent to any boundary of the codedpicture; and decoding the coded picture based on the plurality of CTUs,wherein the at least one row or column of CTUs includes a first CTU rowor a first CTU column of the coded picture that is adjacent to a topboundary or left boundary of the coded picture, respectively, andwherein: the at least one row or column of CTUs includes the first CTUcolumn that is adjacent to the left boundary of the coded picture and alast CTU column that is adjacent to a right boundary of the codedpicture, and the first CTU column and the last CTU column each have awidth that is smaller than a width of each CTU among the plurality ofCTUs that is not adjacent to any boundary of the coded picture, or theat least one row or column of CTUs includes the first CTU row that isadjacent to the top boundary of the coded picture and a last CTU rowthat is adjacent to a bottom boundary of the coded picture, and thefirst CTU row and the last CTU row each have a height that is smallerthan a height of each CTU among the plurality of CTUs that is notadjacent to any boundary of the coded picture.
 2. The method of claim 1,wherein each CTU among the plurality of CTUs that is not adjacent to anyboundary of the coded picture has a same size.
 3. The method of claim 2,wherein the at least one row or column of CTUs includes the first CTUcolumn that is adjacent to the left boundary of the coded picture andthe last CTU column that is adjacent to the right boundary of the codedpicture, and the first CTU column and the last CTU column each have awidth that is smaller than a width of each CTU among the plurality ofCTUs that is not adjacent to any boundary of the coded picture.
 4. Themethod of claim 3, wherein the at least one row or column of CTUsfurther includes the first CTU row that is adjacent to the top boundaryof the coded picture and the last CTU row that is adjacent to the bottomboundary of the coded picture, and the first CTU row and the last CTUrow each have a height that is smaller than a height of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture.
 5. The method of claim 2, wherein the at least one row orcolumn of CTUs includes the first CTU row that is adjacent to the topboundary of the coded picture and the last CTU row that is adjacent tothe bottom boundary of the coded picture, and the first CTU row and thelast CTU row each have a height that is smaller than a height of eachCTU among the plurality of CTUs that is not adjacent to any boundary ofthe coded picture.
 6. The method of claim 1, wherein the decoding thecoded picture comprises signaling the size dimension of the first CTUrow or the first CTU column, from among the at least one row or columnof CTUs, that is adjacent to the top boundary or the left boundary ofthe coded picture.
 7. The method of claim 1, wherein the size dimensionof the first CTU row or the first CTU column is a positive integer thatis a power of
 2. 8. The method of claim 1, wherein the decoding thecoded picture comprises: signaling a first flag that indicates whetherthe size dimension of the first CTU row or the first CTU column, fromamong the at least one row or column of CTUs, that is adjacent to theleft boundary or the top boundary of the coded picture is equal to amaximum allowed CTU size; determining, based on the first flag, that thesize dimension of the first CTU row or the first CTU column is not equalto the maximum allowed CTU size; and signaling, based on thedetermining, a second flag that indicates the size dimension of thefirst CTU row or the first CTU column.
 9. The method of claim 1, whereinthe decoding the coded picture comprises: disallowing horizontal orvertical splitting at CTU level in the first CTU row or the first CTUcolumn of the coded picture, from among the least one row or column ofCTUs, based on determining that the size dimension of the first CTU rowor the first CTU column is equal to or larger than a predetermined valueand another size dimension of the first CTU row or the first CTU columnfrom among the least one row or column of CTUs is smaller than thepredetermined value, wherein the size dimension is one from among heightand width, and the another size dimension is the other from among theheight and the width, and the predetermined value is a power of 2 valuethat is greater than
 64. 10. The method of claim 1, wherein the decodingthe coded picture comprises: disallowing horizontal triple tree (TT) orvertical TT splitting at CTU level in the first CTU row or the first CTUcolumn of the coded picture, from among the least one row or column ofCTUs, based on determining that the size dimension of the first CTU rowor the first CTU column is equal to or larger than a predetermined valueand another size dimension of the first CTU row or the first CTU columnfrom among the least one row or column of CTUs is smaller than thepredetermined value, wherein the size dimension is one from among heightand width, and the another size dimension is the other from among theheight and the width, and the predetermined value is a power of 2 valuethat is greater than
 64. 11. The method of claim 1, wherein the heightof the first or last CTU row is smaller than a maximum CTU size, andeach CTU among the plurality of CTUs that is not adjacent to anyboundary of the coded picture has a height that is equal to the maximumCTU size, a decision on whether the first or last CTU row is smallerthan other CTUs is indicated by one syntax in a bitstream, or the widthof the first or last CTU column is smaller than the maximum CTU size,and each CTU among the plurality of CTUs that is not adjacent to anyboundary of the coded picture has a width that is equal to the maximumCTU size, a decision on whether the first or last CTU column is smallerthan other CTUs is indicated by one syntax in the bitstream.
 12. Asystem comprising: at least one memory configured to store computerprogram code; and at least one processor configured to access thecomputer program code and operate as instructed by the computer programcode, the computer program code comprising: decoding code configured tocause the at least one processor to decode a coded picture that ispartitioned into a plurality of coding tree units (CTUs), wherein atleast one row or column of CTUs, among the plurality of CTUs of thecoded picture, that is adjacent to a boundary of the coded picture has asize dimension that is smaller than a corresponding size dimension ofeach CTU among the plurality of CTUs that is not adjacent to anyboundary of the coded picture, the decoding code is configured to causethe at least one processor to decode the coded picture based on theplurality of CTUs, the at least one row or column of CTUs includes afirst CTU row or a first CTU column of the coded picture that isadjacent to a top boundary or left boundary of the coded picture,respectively, and wherein: the at least one row or column of CTUsincludes the first CTU column that is adjacent to the left boundary ofthe coded picture and a last CTU column that is adjacent to a rightboundary of the coded picture, and the first CTU column and the last CTUcolumn each have a width that is smaller than a width of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture, or the at least one row or column of CTUs includes the firstCTU row that is adjacent to the top boundary of the coded picture and alast CTU row that is adjacent to a bottom boundary of the coded picture,and the first CTU row and the last CTU row each have a height that issmaller than a height of each CTU among the plurality of CTUs that isnot adjacent to any boundary of the coded picture.
 13. The system ofclaim 12, wherein each CTU among the plurality of CTUs that is notadjacent to any boundary of the coded picture has a same size.
 14. Thesystem of claim 13, wherein the at least one row or column of CTUsincludes the first CTU column that is adjacent to the left boundary ofthe coded picture and the last CTU column that is adjacent to the rightboundary of the coded picture, and the first CTU column and the last CTUcolumn each have a width that is smaller than a width of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture.
 15. The system of claim 14, wherein the at least one row orcolumn of CTUs further includes the first CTU row that is adjacent tothe top boundary of the coded picture and the last CTU row that isadjacent to the bottom boundary of the coded picture, and the first CTUrow and the last CTU row each have a height that is smaller than aheight of each CTU among the plurality of CTUs that is not adjacent toany boundary of the coded picture.
 16. The system of claim 13, whereinthe at least one row or column of CTUs includes the first CTU row thatis adjacent to the top boundary of the coded picture and the last CTUrow that is adjacent to the bottom boundary of the coded picture, andthe first CTU row and the last CTU row each have a height that issmaller than a height of each CTU among the plurality of CTUs that isnot adjacent to any boundary of the coded picture.
 17. The system ofclaim 12, wherein the decoding code is further configured to cause theat least one processor to signal the size dimension of the first CTU rowor the first CTU column, from among the at least one row or column ofCTUs, that is adjacent to the top boundary or the left boundary of thecoded picture.
 18. The system of claim 12, wherein the decoding code isfurther configured to cause the at least one processor to: signal afirst flag that indicates whether the size dimension of the first CTUrow or the first CTU column, from among the at least one row or columnof CTUs, that is adjacent to the left boundary or the top boundary ofthe coded picture is equal to a maximum allowed CTU size; based on thefirst flag, that the size dimension of the first CTU row or the firstCTU column is not equal to the maximum allowed CTU size; and signal,based on the determining, a second flag that indicates the sizedimension of the first CTU row or the first CTU column.
 19. The systemof claim 12, wherein the decoding code is further configured to causethe at least one processor to: disallow horizontal or vertical splittingat CTU level in the first CTU row or the first CTU column of the codedpicture, from among the least one row or column of CTUs, based ondetermining that the size dimension of the first CTU row or the firstCTU column is equal to or larger than a predetermined value and anothersize dimension of the first CTU row or the first CTU column from amongthe least one row or column of CTUs is smaller than the predeterminedvalue, wherein the size dimension is one from among height and width,and the another size dimension is the other from among the height andthe width, and the predetermined value is a power of 2 value that isgreater than
 64. 20. The system of claim 12, wherein the decoding codeis further configured to cause the at least one processor to: disallowhorizontal triple tree (TT) or vertical TT splitting at CTU level in thefirst CTU row or the first CTU column of the coded picture, from amongthe least one row or column of CTUs, based on determining that the sizedimension of the first CTU row or the first CTU column is equal to orlarger than a predetermined value and another size dimension of thefirst CTU row or the first CTU column from among the least one row orcolumn of CTUs is smaller than the predetermined value, wherein the sizedimension is one from among height and width, and the another sizedimension is the other from among the height and the width, and thepredetermined value is a power of 2 value that is greater than
 64. 21. Anon-transitory computer-readable medium storing computer instructionsthat are configured to, when executed by at least one processor, causethe at least one processor to: decode a coded picture that ispartitioned into a plurality of coding tree units (CTUs), wherein atleast one row or column of CTUs, among the plurality of CTUs of thecoded picture, that is adjacent to a boundary of the coded picture has asize dimension that is smaller than a corresponding size dimension ofeach CTU among the plurality of CTUs that is not adjacent to anyboundary of the coded picture, the computer instructions are configuredto cause the at least one processor to decode the coded picture based onthe plurality of CTUs, the at least one row or column of CTUs includes afirst CTU row or a first CTU column of the coded picture that isadjacent to a top boundary or left boundary of the coded picture,respectively, and wherein: the at least one row or column of CTUsincludes the first CTU column that is adjacent to the left boundary ofthe coded picture and a last CTU column that is adjacent to a rightboundary of the coded picture, and the first CTU column and the last CTUcolumn each have a width that is smaller than a width of each CTU amongthe plurality of CTUs that is not adjacent to any boundary of the codedpicture, or the at least one row or column of CTUs includes the firstCTU row that is adjacent to the top boundary of the coded picture and alast CTU row that is adjacent to a bottom boundary of the coded picture,and the first CTU row and the last CTU row each have a height that issmaller than a height of each CTU among the plurality of CTUs that isnot adjacent to any boundary of the coded picture.